Many food articles are packaged within a plastic bag and, to extend the period of time during which such items can be stored and to minimize the need for refrigeration, the atmosphere within the bag, which initially is air, is withdrawn and replaced by a selected gas. Thereafter, the bag is completely sealed whereby the food articles within the bag are protected from spoilage.
The field to which this invention pertains is a method and machine for heat sealing a bag and for providing, in conjunction therewith, the exchange of the atmosphere within the bag.